Re: [bg-linux] [PATCH 3/7] [RFC] add support for BlueGene/P FPU

On 05/19/2011 08:53 AM, Eric Van Hensbergen wrote:

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 +#ifdef CONFIG_BGP
 +#define SAVE_FPR(n, b, base) li b, THREAD_FPR0+(16*(n)); STFPDX(n, base, b)
 +#define REST_FPR(n, b, base) li b, THREAD_FPR0+(16*(n)); LFPDX(n, base, b)

       

 16*?  Are these FP regs 64 or 128 bits wide?  If 128 you are doing to
 have to play with TS_WIDTH to get the size of the FPs correct in the
 thread_struct.

 I think there's a bug here.

I actually have three different versions of this code from different
source patches that I'm drawing from - so your help in figuring out
the best way to approach this is appreciated.  The kittyhawk version
of the code has 8* instead of 16*.  According to the docs:
"Each of the two FPU units contains 32 64-bit floating point registers
for a total of 64 FP registers per processor." which would seem to
point to the kittyhawk version - but they have a second SAVE_32SFPRS
for the second hummer.  What wasn't clear to me with this version of
the code was whether or not they were doing something clever like
saving the pair of the 64-bit FPU registers in a single 128-bit slot
(seems plausible).

Yes, it does.    SIMD like instructions are added to BGP PPC.
stdpdx or lfpdx, for example, handle two FPU registers (primary and 
secondary).

Thanks,
Kaz